    /* 基础选择器：（优先级）通配符选择器 < 标签选择器 < 类选择器（最常用） < ID选择器 */
    * {
      font-family: 'Times New Roman', Times, serif;
    }

    div {
      background-color: bisque;
      font-size: 20px;
    }

    .burlywood {
      color: burlywood;
    }

    .red {
      color: red;
    }

    .bg-burlywood {
      background-color: burlywood;
    }

    .bg-red {
      background-color: red;
    }

    .ss-font {
      font-size: 28px;
      font-family: 'Trebuchet MS', 'Lucida Sans Unicode', 'Lucida Grande', 'Lucida Sans', Arial, sans-serif;
    }

    .square {
      width: 100px;
      height: 100px;
    }

    .circle {
      width: 100px;
      height: 100px;
      border-radius: 50%;
    }

    #nav {
      text-align: center;
      background-color: unset;
    }

    .com-font {
      font: italic 700 16px 'Microsoft YaHei';
    }

    h1 {
      text-align: center;
      text-decoration: underline;
    }

    a {
      text-decoration: unset;
    }

    div>p {
      text-indent: 2em;
      line-height: 25px;
    }